2013年内蒙古通辽MS5.3地震震源区地壳速度结构与孕震环境  

Crustal velocity structure and seismogenic environments in the source areas of the 2013 Tongliao, Inner Mongolia, MS5.3 earthquake

作　　者：宋晓燕 雷建设[2] SONG XiaoYan;LEI JianShe(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Key Laboratory of Crustal Dynamics,National Institute of Natural Hazards,Ministry of Emergency Management of China,Beijing 100085,China;Inner Mongolia Autonomous Region Seismological Bureau,Hohhot 010010,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]应急管理部国家自然灾害防治研究院(地壳动力学重点实验室),北京100085 [3]内蒙古自治区地震局,呼和浩特010010

出　　处：《地球物理学报》2022年第10期3912-3929,共18页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(U1939206);国家重点研发计划项目(2018YFC1504103)资助。

摘　　要：为了解2013年内蒙古通辽M5.3地震震源区地壳速度结构与孕震环境,本研究基于“中国地震科学台阵——华北地区东部”29个流动地震台站自2017年1月至2019年4月期间记录的连续波形数据,应用面波直接反演背景噪声成像方法,获得通辽地震震源区与周边地区地壳三维S波速度结构.结果显示,通辽M5.3地震震源区与周边地区地壳S波速度结构呈现明显横向不均匀性.浅层S波速度结构分布特征与地表地质构造密切相关:盆地内侧呈明显低速异常,可能反映了沉积层结构,而大兴安岭下方则呈现明显高速异常,可能反映了造山带较为致密的古生代结晶基底岩.在中下地壳,震源区低速异常向西南方向延展至南北重力梯度带.通辽M5.3地震与该区域速度结构存在密切关系,地震震中位于低速异常边缘,表明该低速异常可能代表深部流体作用降低断层面有效正应力从而触发地震.结合前人全球的和区域尺度的地震层析成像结果展示上地幔存在明显低波速异常与地幔转换带存在明显高波速异常,推测通辽M5.3地震的发生可能与太平洋板块深俯冲至我国东北地区下方地幔转换带内形成“大地幔楔”中结构与动力学密切相关.在“大地幔楔”结构中,由于地幔转换带中滞留板块脱水作用和地幔角流作用,容易形成湿热物质上涌,进而引起松辽盆地西南部岩石圈物质拆沉和携带流体的地幔热湿物质上涌至地壳后作用于断裂带、降低了断层面有效正应力,从而导致了中强度地震的发生.To understand the crustal velocity structure and seismogenic environment of the 2013 Tongliao, Inner Mongolia, M5.3 earthquake, we obtain a 3-D S-wave velocity structure of the crust around the Tongliao earthquake source areas by applying the direct ambient-noise surface-wave tomography technique to the continuous waveform data recorded at the 29 portable seismic stations of eastern North China ChinArray during January 2017 to April 2019. Our results show that there are obvious lateral heterogeneities in the S-wave velocity structure around the Tongliao M5.3 earthquake source areas at the shallow crust. There is a close relationship between the shallower structural features and surface geological tectonics. Obvious low-velocity anomalies are imaged under the inner side of the Songliao basin, likely reflecting the sedimentary structure, whereas obvious high-velocity anomalies appear under the Great Xing′an range, possibly denoting dense Palaeozoic crystalline basement. In the mid-lower crust, the low-velocity anomalies extend southwestward to the North-South Gravity Lineament. The Tongliao M5.3 earthquake is closely related to the regional crustal velocity structure. The epicenter of the Tongliao M5.3 earthquake is located at the boundary of low-velocity anomalies, suggesting that the low-velocity anomalies may denote the deep fluids that could decrease the effective normal stress of the fault planes to trigger the earthquakes. Integrating with previous global and regional upper-mantle tomographic results showing low-velocity anomalies in the upper mantle and high-velocity anomalies in the mantle transition zone, we propose that the Tongliao M5.3 earthquake could be related to the structure and dynamics of the big mantle wedge caused by the deep subduction of the Pacific slab down to the mantle transition zone. In the big mantle wedge structure, due to the stagnancy and dehydration of the Pacific slab in the mantle transition zone or the corner flow, it is easy to generate hot and wet mantle upwelling, leading t

关 键 词：背景噪声面波直接成像方法 通辽地震 地壳速度结构 孕震环境 

分 类 号：P315[天文地球—地震学]